For the purpose of learning the condition of the pneumatic function and electrolyte metabolism of the human body, measurement must be made by blood gas analysis of the respective amounts of oxygen saturation of pH of the arterial blood. Quantitative tests for the electrolyte components in blood may be made simultaneously. In such a blood test, contact of the blood sample to be tested with air or the incorporation of air into the blood sample has an undesirable effect upon the measured value in that the measured value is altered from the true condition of the arterial blood. In its simplest aspects, blood gas analysis is primarily a measurement of PO.sub.2 and PCO.sub.2 in the arterial blood. In this context, the P stands for the partial pressure of the particular gas in the blood. Additionally, a pH determination is usually made. This is a "STAT" procedure. If any time at all elapses between collection and processing, the sample must be iced. Contact of the sample with air has two effects. In the first place, the contact of the sample with oxygen will tend to increase the PO.sub.2 reading. Simultaneously, some of the CO.sub.2 in the blood sample may be lost and this will lower the PCO.sub.2 reading. In short, contamination of the blood sample with air makes a disproportionate change inthe results obtained by raising the PO.sub.2 reading and lowering the PCO.sub.2 reading. Normally, an anticoagulant such as heparin is utilized to prevent coagulation of the sample in the shank portion of the needle or in the syringe proper. Additionally, the anticoagulant has the dual purpose of occupying the dead space in a syringe and further of lubricating the moement of the plunger within the barrel.